Priyasindhu Talukdar, a government official in Rangpur, said Kunio was buried in a Muslim graveyard, adding, “We got confirmation that he had converted to Islam before his death.”

“We held his funeral prayer and then buried him in the graveyard in accordance with Muslim rites. The Japanese embassy in Bangladesh approved the burial and two Japanese officials were present,” Talukdar told AFP.

Japanese embassy spokesman Takeshi Matsunaga confirmed Kunio had been buried in Bangladesh. Bangladesh prides itself on being a mainly moderate Muslim country.

But the gruesome killings of a series of atheist bloggers this year have rocked the nation and sparked a crackdown on local hardline Islamist groups.

Experts say militants pose a growing danger in Bangladesh, warning that a long-running political crisis has radicalised opponents of the government.

However, experts have also expressed scepticism about the IS claim of responsibility in the murders of Kunio and Tavella.